If your first friendly reminder did not work then sending a second friendly reminder will likely be received with their second silent "sc**w you".Friendly reminders rarely get results, unfortunately you have to 'play the game" but ultimately you must be very strict, clearly define your requirements and the consequences of not complied.

Sometimes I think it's our job in the universe to provide someone with a consequence.  

Now, if she was stuffing "flushable" wipes, and we all know there really is no such thing, and you've explained to her that she can't flush flushable wipes and if it happens again and the snake brings up a wad of flushable wipes again - then she'll have to pay the bill - that's reasonable.But, to charge her for a problem because you can't figure out how it's happening - well, you'll end up with an expensive consequence.  

Sometimes I think it's our duty in life to be someone's consequence.  

And so far, the only real thing that's happened, is a tenant asked if they could break the lease without consequence.  

The consequences of not protect your business by mitigate risk in whatever way necessary are far higher.I have had a couple of slaps on the wrist, never serious, and always well worth it.

As @Mike Hanneman has said: figure out what you want, i.e. either keep it as a rental (and consequently raise the rent; all these matters you should communicate in a proper way, which I consider - especially in that situation - in paperform via snailmail) or you moving back in.

Or face the drama and consequences, which will be many.

Risk is defined as uncertainty in the outcome of events (or probability x consequence). 

It best to make everyone responsible for what they consume and if they don't pay, they bare the full consequence.